bagyoudaoicibaDictYouDict[bag 词源字典]
bag: [13] English acquired bag from Old Norse baggi ‘bag, bundle’, but it does not appear in any other Germanic language, which suggests that it may have been borrowed at some point from a non-Germanic language. Forms such as Old French bague, Italian baga, and Portuguese bagua show that it existed elsewhere. A derivative of the Old French word was bagage, from which in the 15th century English got baggage; and Italian baga may have led, by a doubling of diminutive suffixes, to bagatella ‘insignificant property, trifle’, which entered English in the 17th century via French bagatelle (although this has also been referred to Latin bacca ‘berry’ – see BACHELOR).
=> bagatelle, baggage[bag etymology, bag origin, 英语词源]
bag (n.)youdaoicibaDictYouDict
c. 1200, bagge, from Old Norse baggi or a similar Scandinavian source; not found in other Germanic languages, perhaps ultimately of Celtic origin. Disparaging slang for "woman" dates from 1924 (though various specialized senses of this are much older). Meaning "person's area of interest or expertise" is 1964, from Black English slang, from jazz sense of "category," probably via notion of putting something in a bag.

To be left holding the bag (and presumably nothing else), "cheated, swindled" is attested by 1793. Many figurative senses, such as the verb meaning "to kill game" (1814) and its colloquial extension to "catch, seize, steal" (1818) are from the notion of the game bag (late 15c.) into which the product of the hunt was placed. To let the cat out of the bag "reveal the secret" is from 1760.
bag (v.)youdaoicibaDictYouDict
mid-15c., "to swell out like a bag;" also "to put money in a bag," from bag (n.). Earliest verbal sense was "to be pregnant" (c. 1400). Of clothes, "to hang loosely," 1824. For sense "catch, seize, steal," see bag (n.). Related: Bagged; bagging.